Thermoelectric generator with radioactive material heat source

ABSTRACT

An electrical generator having an Isotopic Heat Capsule including radioactive fuel rod 21 as a primary heat source and Thermoelectric Modules 41 and 43 as converters. The Biological Shield for the Capsule is suspended from Spiders at each end each consisting of pretensioned rods 237 and 239 defining planes at right angles to each other. The Modules are mounted in cups 171 of transition members 173 of a heat rejection Fin Assembly whose fins 195 and 197 extend from both sides of the transition member 173 fore effective cooling.

J l 2, 1974 D. L. PURDY EI'AL 3 322 151 THERMOELECTRIC GENERATOR WITHRADIOACTIVE MATERIAL HEAT SOURCE Original Filed Dec. 14, 1966 7Sheets-Sheet l Q I I 254 Q 237 3|3 Q Q 289 i H 287 Q I 303 I97 za 3 Fl6. I.

July 2, 1974 I 3,222,151

THERMOELECTRIC GENERATOR WITH RADIOACTIVE MATERIAL HEAT SOURCE v D. L.PURDY ETAL Jul 2, WM

THERMOELECTRIC GENERATOR WTL'IH RADIOACTIVE MATERIAL HEAT SOURCEOriginal Filed Dec. 14, 1966 7 Sheets-Sheet S FIG.3.

' D. L. PURDY ETAL July 2, 1974 THERMOELECTRIC GENERATOR WITHRADIOACTIVE MATERIAL HEAT SOURCE 7 Sheets-Sheet 4 Original Filed Dec.14, 1966 July 2, 1974 i PURDY 3,822,151

THERMOELECTRIC GENERATOR WITHRADIOACTIVE MATERIAL HEAT SOURCE OriginalFiled Dec. 14, 1966 '7 Sheets-Sheet 5 THERMOELECTRIC GENERATOR WITHRADIOACTIVE MATERIAL HEAT SOURCE Original Filed Dec. 14, 1966 7Sheets-Sheet 6 D. L. PURDY ETML THERMOELECTRIC GENERATOR WITHRADIOACTIVE MATERIAL HEAT SOURCE 7 Sheets-Sheet 7 Original Filed Dec.14, 1966 ii in a. .5

105- 3 UH Pin 1 0U UHQ HONQAOHOM UHOH ii 3 2. wnomonomoi unfifi iiiiiiFIG.9.

FIG.IQO.

3,822,151 THERMOELECTRIC GENERATOR WITH RADHO- ACTIVE MATERIAL HEATSOUREIE David L. Purdy, Indiana, Zalman M. Shapiro, Pittsburgh, ThomasF. Hui-sen, Mo'nroeville, and Gerould W. Maurer, Apollo, Pa., assignorsto Arco Nuclear Continuation of abandoned application Ser. No. 601,697,Dec. 14, 1966. This application May 10, 1971, Ser. No. 142,070

Int. Cl. H01v ]/30, 1/32 US. (1]. 136-202 8 Claims ABSTRACT OF THEDISCLOSURE GENERATOR This application is a continuation of applicationSer. No. 601,697, filed Dec. 14, 1966, now abandoned.

This invention relates to the generation of electricity and hasparticular relationship to electrical generators particularly for use inspace or in remote parts of the earth where commercial power is notavailable or within the human body. Such generators typically include anisotopic heat source or capsule including a radioactive isotope, such asstrontium 90, cobalt 60 or plutonium 238, which serves as a primarysource of energy and a heat-to-electricity converter in heat-interchangerelationship with the capsule. Electricity is derived from theconverter. The capsule is enclosed in a biological shield. The convertertypically consists of one or more thermoelectric modules each having ahot junction thermally connected to the shield through a heat-transferassembly, and a cold junction thermally connected to heat-rejectionassembly. Supporting structure is provided for the capsule, heat shield,modules and heat-rejection assembly.

It is necessary that the capsule and biological shield be suspended fromthe supporting structure. Typically, this suspension is a spider ofelongated members which thermally shunts the connection of the shield otthe cold junction. Since the energy from the primary source must beconserved, it is essential that the thermal conduction of thissuspension to the support be minimized. But it is also necessary thatthis suspension have high strength and high impact resistance; thermallyinsulating materials are then not in general suitable for thissuspension. It is an object of this invention to meet the aboveconditions and to provide a generator including a heat capsule in abiological shield in which the suspension from the supporting structurefor the shield and capsule shall be of high strength and high impactresistance and whose thermal conduction of heat from the shield to thesupporting structure shall be minimized.

In arriving at the aspect of this invention involving the suspension ithas been realized that the shield and capsule may be convenientlysuspended by spiders extending from opposite sides of the capsule, eachspider including three elongated members. Where the shield is in theform generally of an elongated cylinder, the spiders may extend from theends of the shield. It has further been realized that to minimize theheat flow to the supporting structure the elongated members of eachspider should be so posi- 3,822,151 Patented July 2, 1974 tioned thatthe pairs of these members define three different planes, the planesbeing mutually substantially at right angles to each other. Inaccordance with this invention a generator is provided having a shieldsuspended by sets of three elongated members each, extending fromopposite sides of the shield, the pairs of members of each set definingplanes which are mutually substantially at right angles to each other.

Another aspect of this invention arises from the realization that theelongated members are heated by the shield to which they are connectedand that the resulting thermal expansion of the shield may cause thesemembers to sag and reduce their suspending effectiveness. It is anobject of this invention to overcome this deficiency of the suspension.In accordance with this invention the elongated members are pretensionedto an extent such that the pretensioning compensates for the expansionand prevents the sagging. The pretensioning is eifected by a nut 'Whichdefleets a strip or band in dependence upon the pretensioning. Theextent of the pretensioning may be determined by measuring thedeflection of the band.

An object of this invention is to provide a generator whosethermoelectric modules may be readily replaced. Such ready replacementpresents difficulties because of the tendency of the heat transferassembly for the hot junction to diffusion bond to the parts with whichit is in heattransfer relationship. The heat-transfer assembly includesa saddle of a highly conducting material, such as copper, which isbrazed to the shield. Heat is transferred from this saddle to the hotjunction through a corrosion-resistant plate which transfers heat to asecond corrosion-resistant plate that serves as a cap for the module andengages an electrically insulating, but thermally conducting, sheetbetween the hot junction and corrosion-resistant means. Thecorrosion-resistant means may be a nickel-base alloy such as Hastelloy-C(see page 173, Materials in Design Engineering-Materials SectionIssue1965). To achieve effective transfer of heat from the shield to thehot junction of the module, it is necessary that substantial pressure bemaintained between the hot junction and the shield through theheat-transfer assembly.

A11 aspect of this invention arises from the realization that thispressure would diffusion bond the corrosionresistant plate to the saddlewhich it engages and to the other corrosion-resistant plate and isdirected to the prevention of such bonding.

In accordance with this invention a plate or sheet of good thermallyconducting material coated on both sides Wiht gold or other goodthermally conducting material is interposed between thecorrosion-resistant plates. Typically the sheet may be composed ofalumina (A1 0 While the gold diffusion bonds to the corrosion-resistantmaterial, it is separable from the sheet to which it does not bond. Themodule with its cap may then be readily removed for replacement from thegenerator.

Another aspect of this invention arises from the necessity of providingan adequate and effective heat sink or heat-rejection assembly for thecold junction and it is an object of this invention to provide agenerator with such a heat sink. In accordance with this invention thegenerator includes a heat sink including a central fin transition memberin heat-interchange relationship with the cold junction of each module.Fins extend from both opposite faces of this member and effectivelytransfer the heat from the cold junction. The fin-transition member hasa cup intermediate its ends which holds the shock-absorbing and pressureapplying mechanisms for the associated module at the same time providingfor effective heat rejection.

Typically the shield may be generally cylindrical with a pair or pairsof thermoelectric modules extending diametrically from its side wall andwith diametrical fin assemblies with the cups of each fin-transitionmembers 3 supporting the shock-absorbing and pressure-applying mechanismfor each module.

Each tin-assembly is hinged at one end so that it may be removed. Thefin-assembly is usually very heavy (typically about 120 pounds for a 50watt generator) and a double-acting hinge is provided to facilitateremoval.

For a better understanding of this invention, both as to itsorganization and as to its method of operation, together with additionalobjects and advantages thereof, reference is made to the followingdescription taken in connection with the accompanying drawing, in which:

FIG. 1 is a view in perspective of a generator according to thisinvention with a part removed to show the inner components;

FIG. 2 is a plan view of this generator with parts broken away andsectioned;

FIG. 3 is a view in section taken along line IIIIII of FIG. 2;

FIG. 3A is an enlarged fragmental view of FIG. 3;

FIG. 4 is a diagrammatic view showing the spider suspension for thebiological shield of the generator shown in FIG. 1;

FIG. 5 is a plan view of a fin assembly for a module showing in brokenlines the manner in which this assembly is moved to afiord access to themodule;

FIG. 6 is a plan view of the hinge of the fin assembly;

FIG. 7 is an end view of this hinge;

FIG. 8 is a view taken along line VIIIVIII of FIG. 7;

FIG. 9 is a side view of a thermoelectric module, with a part brokenaway, used in the practice of this invention;

FIG. 10 is a section of this module taken along line XX of FIG. 9; and

FIG. 11 is a plan view of a component of a shock absorber used in thepractice of this invention.

The generator shown in the drawings includes an Isotopic Heat Capsule,which serves as primary source of energy, a Biological Shield enclosingthe Capsule, a Thermoelectric Module engaged in heat interchangerelationship with diametrically opposite faces of the shield, aRadiation Heat Shield around the Biological Shield, a Fin Assembly ineffective heat-rejection relationship with the cold junction of eachModule.

The Capsule, Biological Shield, and Radiation Heat Shield are enclosedin a Casing which has re-entrant portions for the Modules and includessupporting rings 11 and 13 for the Biological Shield at opposite ends.The Biological Shield and Capsule are suspended from these rings 11 and13 by Spiders.

The Capsule includes a fuel rod or bar 21 of a radioactive isotope,typically strontium titanate whose strontium is SR 90. The bar 21 isenclosed in a casing-23 typically of T111 alloy (Ta, w. 8%, Hf 2.5%)which is com patible at high temperatures with the strontium titanateand has impact strength at high temperatures. This casing 23 is enclosedin a casing 25 of Hastelloy-C alloy which is corrosion-resistant.

The Biological Shield includes a generally cylindrical mass 31 ofKerrnertium W4 alloy (97.6% w. and 2.4% copper and nickel) described inleaflet L-502 of Kennametal, Inc., Latrobe, Pa. The mass 31 has acentral cavity for the Capsule accessible through a stepped opening inone end through which the Capsule is inserted. The opening is sealed bya stepped plug 33 having flanges 35 bolted to the part of the mass 31adjacent the plug. The plug 33 is a slip fit in the opening and when theplug 33 and adjacent metal are heated by the Capsule the plug 33 iswelded to the boundary of the opening. Shims 37 (FIG. 2) of copper arebrazed along diametrical opposite surfaces of the mass 31. Saddles 39 ofcopper for connection to the Thermoelectric modules are brazed atdiametrical positions of the mass 31 between the shims 37.

The heat of the Capsule is converted into electricity by Modules 41 and43 mounted at opposite diametrical positions of the Shield with theshield in good heat trans- 1 fer relationship with the hot junctionshoes 45 of the Module.

Each Module 41 and 43 includes a cylindrical block 51 (FIGS. 9 and 10)of aluminum having a plurality of pairs of longitudinal holes 52corresponding in number to the pairs of positive and negativesemiconductor pellets 53 and 55 respectively which the Module is toinclude. The walls of each hole is oxidized so that it is electricallyinsulating. In each hole there is an electrically insulating supportwasher 56, a spring 57, a plug or follower 59 of aluminum, and end caps61 and 63, and a positive or negative pellet 53 or 55, as the case maybe. Typically, the pellets are of doped lead-telluride and the end caps61, 63 are of copper-tellurium alloy. The washers 56 and springs 57 areheld in the holes 52 by wires 71 extending across the block 51 generallyalong diameters of the holes. Each spring 57 seats in a shoulder in aplug 59 and urges the plug into firm electrical and thermal contact withthe associated end cap 61 or 63 in turn urging the end cap into firmthermal and electrical engagement with the associated pellet 53 or 55.Each pair of pellets 53 and 55 is connected at the top by a hot-junctionshoe 45. The end cap 63 of a pellet 55 of each pair is connected by astrap 73 to the end cap 61 of the pellet 53 of an adjacent cap. Thepellet couples 53-55 are thus connected in series through their coldjunctions by the straps 73.

The block 51 is sealed in a cylindrical casing composed of a shell 75and bases 77 and '79 of Hastelloy-C alloy. The casing 75-7749 is filledwith argon or other inert gas which has a pressure of about oneatmosphere when the apparatus is in use, to protect the pellets 53 and55, and is sealed by electron-beam welding at the junctions of the shell75 and the bases 77 and 79. An electrically insulating sheet 80 isinterposed between the shoes 45 and the base 77.

The shell 75 is provided at the inner end (towards the Shield) withsegments 82 consisting of alumina coated with gold. When the Module ismounted in the generator these segments 79 are in engagement with theadjacent parts of the generator. The gold bonds to these parts but thealumina may be separated from the gold permitting the Module to beremoved.

On the outside of the shell 75 at the outer end (away from theBiological Shield) there is a power take-off assembly 81 includingterminals 83 and 85 connected respectively to the cold junction of thefirst and last couple of the series aggregate of pellets 53 and 55.These terminals 83 and 85 are in a potting compound (Silicone) and areconnected to wires in cables 87 and 88 from which the power is derived.The cables 87 and 88 are connected to output cables 89 through adisconnectible junction 91 (FIG. 3A). The cables 91 are sealedpressure-tight through the Casing and are connected to a voltage-controlbox (FIG. 2) including a conventional voltage regulator 102. The box 100has an output converter 1 10 and cable 106 from which power may bederived.

Each Module 41 and 43 is connected in good heattransfer relationship tothe shield through a heat-transfer assembly including a generallyelongated C-shaped plate 93 (FIG. 3A) of Hastelloy-C alloy and thesaddle 39. So that the Module 41 or 43 may be removed a sheet 95 ofalumina coated on both faces with gold is interposed between the base 77and the plate 93. The plate 93 constitutes one end plate of a sylphonassembly 101 by which each Module is resiliently suspended on ashockabsorbing assembly 103 resiliently suspended by another bellowsassembly 104. The plate 93 is secured to the Biological Shield by key105 of Kennertium alloy which engage keyways in the Shield and saddle.The keys 105 are brazed to the plate 93.

The bellows assembly 101 (FIG. 3A) includes a bellows 111 from the outerrim of which a guiding shell 113 extends. The assembly 101 also includesan external supporting ring 115. The bellows 111 is welded, typically byelectron-beam welding, to the plate 93 at the inner end and to aprojection 114 from the ring 115 at the outer end. The ring 115 isprovided with grommets 117 (FIG. 3A, only one shown) through which thecables 89 pass. All the components of bellows assembly 101 are composedof Hastelloy-C alloy.

The bellows assembly 104 includes a bellows 119 and an outer ring 121(FIG. 2) in the form of a bottomless cup. The bellows 119 is sealedbetween a plate 123 and the ring 121. The ring 115 is a tight slidablefit in the cup or ring 121 and is welded to a skirt 241 (FIG. 3) of theCasing. An O-ring 122 is interposed between the ring 115 and the cup orring 121. All the parts of this assembly 104 are composed of Hastelloy-Calloy.

The shock-absorber assembly 103 includes an inner pressure plate 131(FIGS. 3A, 11), which is in engagement with plate 123 that serves as acover plate for the shock-absorber 103, and an outer pressure plate 133.The inner plate 131 has a plurality of circular grooves 135 and theouter plate has a plurality of circular holes 137 (FIG. 3A) coaxial withthe grooves 135. In each hole 135 a locator washer 139 with a shoulderis held by a retaining ring 141. Inner and outer springs 143 and 145rest against the shoulder of each washer 139. The springs 143 and 145resiliently compress the inner plate 131 against the plate 123 which isresiliently movable by reason of the resilience of the bellows 119. Thesprings 143 and 14 5 thus act to compress the block 51 and the shoes 45into firm heat transmitting engagement with the plates 77, 95, 93, thesaddle 39 and the Biological Shield.

The inner and outer plates 133 and 135 include slots 151 (slots in innerplate not shown) extending from the periphery to the center inincreasing length in all quadrants (FIG. 11). The slots 151 in bothplates are aligned. Masses 153 of crinkled copper sheet extend throughthe slots 151 in both plates 131 and 133 with their crinkled surfacesvertically between the inner and outer plates 131 and 133 and are weldedon end to the remote edges of the plate. The plates 131, 133 arecomposed of Copper; the springs 143 and 14 5 are composed of springsteel.

The Casing 75-77-79 and its content is suspended from the bellows 1 11on retaining rings 161 and 163 (FIG. 3A). Retaining ring 161 is a splitring which engages a shoulder 165 of the lower thickend portion 167 ofthe shell 75. The ring 163 is a resilient ring with a slot (not shown)in its periphery which is compressed into a groove in the ring or sleeve115. The ring 163 supports ring 161 which in turn supports the shell 75and its contents.

The bellows 119 is connected at one-end to the base of the ring 121 andat the other end to the plate or sheet 123 and permits the shockabsorbing assembly 153 to support the Module resiliently through plate123 and base 79. The springs 143 and 145 resiliently press the shoes 45into good heat-receiving relationship with the heattransfer assembly 77,95, 93, 39. To improve heat fiow there is a layer of gold between base79 and plate 123.

Each thermoelectric Module is supported in a cupshaped depression 171 ofa transition member 173 of the Fin Assembly. The cup-shaped ring 121 isseated in this depression 171 engaging the sloping walls thereof. Nearthe region 175 where the depression 171 joins the remainder of themember 173 the ring 121 is welded pressure-tight to the member 173. Theshock-absorbing assembly 103 is retained in the depression 171 by rods18]. which are secured along the rim of plate 131 and s-waged throughplate 133 into a hole 183 in the base of portion :171.

The Fin Assembly includes the transition member 173 (FIG. 5). Thismember 173 is composed of a copper core 191 (FIG. 2) for good heatconduction, encased in a cladding 193 (FIG. 3A) of Hastelloy-C alloy forcorrosion resistance and also for satisfactory welding to the ring 121,which is also composed of Hastelloy-C alloy, and for satisfactorybrazing to the fins 195 and 197 which are also composed of Hastelloy-Calloy. The member 173 may be formed by brazing sheets of Hastelloy-Calloy on both bases of a copper plate and then forming the member 173.For brazing a shim of titanium is interposed between the copper and thealloy and the composite sheet-plate structure is heated to brazingtemperature. Typically the core 191 has a thickness of about .350 inchesand the cladding 193 thickness of about .020 inches. The cladding 193 isnot present at the base of the cup 191 which is engaged by the base 133of sylphon 103.

The ends of the member 173 are also encased in cladding of Hastelloy-Calloy. At the ends from which the Pin Assembly is mounted on the Casing,the cladding 201 is of generally C-section having a web substantiallythicker than the other cladding 1193.

The fins 19 5 and 197 are formed from a sheet of Hastelloy-C alloy whichis corrugated into a structure of generally zig-zag section with fiatends 203. The fins and 1 97 extend from both faces of the transitionmember 173 with the flat ends 203 abutting the member 173 brazed to it.Because the fins 195 and 197 are in both sides of the member 173 whichreceives the heat from the cold junction of the Module they efiectivelyabsorb this heat and the heat sink is highly effective.

Each Fin Assembly and the ring 121 joined to it is removably secured tothe Casing. At one end the Pin Assembly is bolted to studs 205 (FIG. 2)extending from the Casing. The bolts 207 pass through tabs 204 (FIG. 5secured in the end cladding 201. At the opposite end each Fin Assemblyis suspended from a hinge 211 (FIGS. 5, 6, 7, 8) including a fixed hingepin 213 secured to the Casing and a plurality of movable hinge pins 215and 217, one 215 pivotally connected to the end of the transition member173 and the other 217 movably suspended between the pins 213 and 215.This hinge permits the removal of the Fin Assembly, which may weigh inexcess of one hundred pounds, from the Casing in two steps as shown inFIG. 5.

The Fin Assemblies are encased in a protective screen 221 which is inpart supported from the fins 195 and in part from fins 223 spot weldedto the Casing. The shell 221 is spot welded to the fins 195 and 223. Thefins 223 serve to support the screen 221 and do not serve for heatremoval purposes.

The Casing includes a cylindrical shell 231 (FIG. 3) of Hastelloy-Calloy having sloping shoulders 233 which flare into short end sections235 of greater diameter than at the center. The rings 11 and 13 arewelded internally to each of the sloping shoulders 235. The rings 11 and13 are composed of high-strength, high-impact resistance alloy so thatthey are capable of withstanding the stress exerted by the rods 237 and239 of the Spiders. Typically the rings 11 and 13 are composed of analloy of titanium having 6% aluminum and 4% vanadium. The shell 231 hasopenings into which the thermoelectric Modules 4 1 and 43 extend.Ring-shaped skirts 241 of Hastelloy-C are welded into these openings.Bands 243 of Hastelloy-C alloy are welded to the outer surface of theshell 231 near the openings to support the Pin Assemblies. These bands243- may be formed of coextensive semi-circular sections. Channelbrackets 245 are welded to the bands 241 and the studs 244- for bolts24-6 are welded to these brackets.

The Casing includes end-cap assemblies 251 and 253 of Hasetelloy-C alloywhich are welded at 254 pressuretight to the runs of the sections 235 ofthe shell 231. Each assembly 251 and 253 includes a cup-shaped plate 255to which fins 250 are spot welded. The fins 250 serve for mounting thesupport leg assembly 256 and 258 and not primarily for cooling. Alifting stud 257 is welded centrally to each of the plates 255, the fins250 extending radially from this stud. The studs 257 are threadedinternally so that an eye-bolt 259 may be inserted for lifting theGenerator.

The leg assemblies 256 and 258 are supported from ring brackets 261welded to the fins 250. Each assembly 256 and 258 is of generallytruncated conical form including a ring 263 bolted to the brackets 261and a ringshaped support base 265, of greater outer and smaller innerdiameter than the ring 263, which is turned up at its rims forstiffness. The rings 263 and 265 are held together by axial plates 271welded to the rings. The rings 263 and 265 and the plates 271 are allcomposed of Hastelloy-C alloy and are all perforated to reduce weight.

The Spiders suspend the Shield at each end from the Casing (FIG. 4).Each Spider includes a plurality of tension rods 237 and 239 (FIG. 1)respectively composed of a resilient high tension material such as asuitable lnconel alloy of iron, nickel, and chromium. The rods 237 or239 at each end extend from a ring 281 of the Ti-GAl-4v alloy, bolted tothe Shield at each end, to the rings 11 and 13 respectively of the samealloy. The rods 237 and 239 are each enlarged at one end 283. Theenlarged ends engage and, are held in enlarged openings in the rings281. Each rod 237 and 239 is threaded at the other end 285. The threadedend 285 of each rod 237 or 239 passes through an opening in a ring 11 or13 and is tensioned by a nut 287. A ring 289 typically of 316 stainlesssteel is interposed between the nut 287 and a recession in the ring 11or '13. The deflection of this ring 289 produced by screwing on the nut287 to tension rods 237 or 239 serves to regulate the tension in therods. The deflection may be measured by a gauge interposed between thering 11 or 13 and the ring 289. The rods 237 and 239 at each endrespectively are so arranged that each pair of each set of rods definesa different plane, the planes being at right-angles to each other (seeFIG. 4).

The Radiation Heat Shield includes a plurality of sheets or foil 301(FIGS. 1, 3, 3A) of an alloy of 88% zirconium and 12% titanium wrappedin overlapping relationship to form a cylindrical wall 303 with taperedrims 305 at the bases. The overlapping is necessary to avoid building upfoil at the joints. Because of the overlapping successive sheets 301must have holes in different positions to accommodate the capsules 41and 43. The Radiation Heat Shield also includes sheets 311 of the samealloy stacked to form truncated conical walls 313 meshing with thetapered ends 315 of the cylindrical wall 303 to form an enclosure. Thesheets or foil 301 and 311 have cross grooves as shown in Pat. 3,607,443granted Sept. 21, 1971 to David L. Purdy for Electrical Generator (FIGS.7 and 8) so that they are in contact only at points to reduce thermalconduction.

The corners between the walls 303 and 313 and the Biological Shield arefilled with gettering wool 321 (FIG. 3) of the Zr 88 Ti 12 alloy. Theregion bounded by the sylphon 111, (FIG. 3A), the plates 93, the rings115, and the Casing is sealed pressure tight and is evacuated. The foil301 and 311 of the Heat Shield and the W001 321 serve as a getter tomaintain the vacuum. The W001 321 is held by getter shields 323 ofmolybdenum.

In the use of the Generator the heat developed by the Capsule istransmitted through the Biological Shield to the hot-junctions of theModules. The cold junctions are cooled by the Pin Assemblies and poweris derived from the Modules.

While a preferred embodiment of this invention is disclosed herein, manymodifications thereof are feasible. This invention then is not to berestricted except insofar as is necessitated by the spirit of the priorart.

What we claim is:

1. A generator of electricity for generating substantial power includinga capsule having a radioactive material which generates adequate heat asa result of the radioactivity of said material to serve as a primarysource of energy for said generator, said material also generatingsubstantial quantities of X-rays, a biological shield completelyenclosing said capsule in heat interchange relationship with saidcapsule, said shield being predominately of a high density, highatomic-number material, and having an adequate mass to substantiallyabsorb said X-rays, a heat-to-electricity converter connected inheat-interchange relationship with said shield to convert said generatedheat into electricity, said converter being of the thermoelectric typeand including solid-state thermoelectric elements, each having a hotjunction and a cold junction, supporting-structure means for saidcapsule, shield and converter, said supporting-structure means includinga heat-sink for said converter comprised of a thermally highlyconducting member of substantial thickness and mass, the solid-statethermoelectric elements of said converter being connected between thesurface of the shield and a surface of extended area of a portion ofsaid member with the hot junctions of said elements in goodheat-interchange relationship with said shield at said surface of saidshield and said cold junctions in good heat-interchange relationshipwith said heat-sink at said surface of said member, and a suspensionconnected between said shield and structure means for suspending saidshield and capsule and including pretensioned rods extending oppositelybetween said shield and said structure and having sufficient strength tosustain the weight of said shield and capsule, the rods beingsufiiciently pretensioned to compensate for the expansion of said rodsas they are heated by the shield and capsule and to prevent said rodsfrom sagging, the said suspension constituting a thermal shunt acrosssaid converter between said shield and heatsink and being so formed andconnected to said shield as to minimize the loss of heat from saidshield resulting from shunt heat flow through said suspension ascompared to the heat flow from said shield through said converter.

2. The generator of claim 1 wherein the pretensioning of the rods issuch as to substantially compensate for the thermal expansion of saidrods as said rods are heated by the shield.

3. The generator of claim 1 wherein the rods are so thin incross-section as to minimize heat leakage therealong from the shield tothe structure while being so strong as to support the shield by exertingsubstantially only tension.

4. The generator of claim 1 including resilient means, interposedbetween the surface of extended area of the portion of the member andthe converter, for urging the thermoelectric elements of the converterinto good heat-interchange relationship with the shield under pressure.

5. The generator of claim 1 including resilient means for urging theconverter into good heat-interchange relationship with the shield underpressure wherein the pressure tends undesirably to diffusion bond theconverter to the shield also wherein the converter includes means forpreventing the said diffusion bonding and permit ready separation of theconverter from the shield for ready replacement of the converter.

6. The generator of claim 1 wherein the resilient means isshock-absorber means interposed between the cold juntions of thethermoelectric elements of the converter and the surface of extened areaof the member, the said shock-absorber means serving as a shock-absorberfor the converter.

7. The generator of claim 1 wherein the thermally highly-conductingmember includes heat rejection fins.

8. The generator of claim 7 wherein the fins extend from the oppositesurface of the member for effective cooling of the member.

References Cited UNITED STATES PATENTS (Other referenees on followingpage) 9 UNITED STATES PATENTS Ray 165-67 X Vollrath 136-221 Elm et a1.136-208 MacFarlane 136-202 X Fritts 136-221 X Callard 165-82 X Nelson136-202 X Banks, Jr. et a1. 136-202 Belofsky 136-202 Brunkrnan et a1.248-18 Stathoplos 136-202 10 OTHER REFERENCES Astro-Electronics Div.R.C.A. TID 222350 (U.S. A.E.C. Pub.), Available to Public November 1965,pp. cover and 9-14.

Corliss et aL: Radioisotopic Power Generation, Prentice-Hall, Inc. NJ.(1964), pp. iii, 12, 118, 119, 124, 126, 128, 207-209 and 216.

ALLEN B. CURTIS, Primary Examiner U.S. Cl. X.R. 136-205, 212

